Tool life, offset, and selection supervision method

ABSTRACT

A tool life supervision method in which the life of a tool is monitored and machining is performed by using another tool when a former tool has reached the end of its life. The tool life supervision method includes the steps of setting in memory means a number of parts to be machined, which number conforms to tool life; setting in the memory means a tool selection number correction value Nct; inserting at an end of an NC machining program at least an instruction or symbol which indicates the end of the program; counting instructions or symbols indicating the end of a program; monitoring whether a counted value coincides with the preset number of parts to be machined and counting the number of times coincidence is achieved; performing the following operation using an arithmetic circuit 110: 
     
         Nt+Nct·n 
    
     wherein n represents the number of times coincidence is achieved, Nt represents a tool selection number indicated by a tool selection instruction in the NC machining program, and Nct represents a tool selection number correction value, and selecting a tool by employing the result of the aforesaid operation as an actual tool selection number.

BACKGROUND OF THE INVENTION

This invention relates to a tool life supervision method and, moreparticularly, to a tool life supervision method in which the life of atool is monitored and machining is performed by using a new tool whenthe former tool has reached the end of its life.

In numerical control (NC) machining tools sustain wear, and when a toolhas reached the end of its life machining can no longer be carried outin the manner commanded. Accordingly, conventional practice, asdisclosed in Japanese Patent Publication No. 51-48825 (Japanese PatentApplication No. SHO 47-80915), is to supervise tool life tool by tooland when a tool reaches the end of its life, to use a succeeding tool inaccordance with a pre-registered sequence For example, the methodincludes monitoring utilization time for a certain tool (namelymachining time using the tool), and employing a new tool when totalutilization time reaches that conforming to a preset tool life.

With the foregoing tool life supervision method, however, (a) tool lifesupervision must be performed tool by tool, and (b) supervision ofutilization sequence must be carried out, wherein a plurality of toolsare prepared with respect to a single tool number, the tool utilizationsequence is registered in advance, and new tools are used in theregistered sequence as the preceding tools reach the end of theirrespective lives. For such reasons, supervision is a complicated matter.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a simplemethod of performing tool life supervision.

Another object of the present invention is to provide a method wherein,rather than requiring tool life supervision to be performed tool bytool, all tools commanded by a single NC machining program can besubjected to tool life supervision en bloc.

A further object of the present invention is to provide a tool lifesupervision method wherein, even though a plurality of identical toolsare assigned different tool numbers, a tool number commanded by an NCmachining program is changed automatically when the tool presently inuse comes to the end of its life, whereby a tool identical with theexpended tool can be selected automatically thereafter.

Still another object of the present invention is to provide a tool lifesupervision method wherein when a tool presently in use comes to the endof its life, a tool identical with the expended tool can be subsequentlyselected by automatically changing a tool number commanded by an NCmachining program, and wherein a tool offset number commanded by an NCmachining program can be changed automatically to a tool offset numberconforming to a selected tool.

The present invention is a tool life supervision method in which thelife of a tool is monitored and machining is performed by using anothertool when a former tool has reached the end of its life. Particularly,the invention provides a tool life supervision method wherein tool lifesupervision for all tools commanded by a single NC machining program canbe performed en bloc so that it is unnecessary to perform tool lifesupervision tool by tool. The tool life supervision method includes thesteps of assigning different tool numbers to a plurality of identicaltools in advance; setting in a memory means, a number of parts to bemachined, which number conforms to tool life, as well as a toolselection number correction value; inserting at the end of an NCmachining program an instruction or symbol which indicates the end ofthe program; counting instructions or symbols indicating the end of aprogram; monitoring whether the counted value coincides with the presetnumber of parts to be machined and counting the number of timescoincidence is achieved; performing the following operation:

    Nt+Nct·n

wherein n represents the number of times coincidence is achieved, Ntrepresents a tool selection number indicated by a tool selectioninstruction in the NC machining program, and Nct represents a toolselection number correction value; and selecting a tool by employing theresult of the aforesaid operation as an actual tool selection number.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first embodiment of the presentinvention;

FIG. 2 is view for explaining a tool selection number of an actuallyselected tool;

FIG. 3 is a view for explaining a tool offset number of an actuallyselected tool;

FIG. 4 is a block diagram of a second embodiment of the presentinvention; and

FIGS. 5A and 5B are flowcharts of processing associated with theembodiment of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings

FIG. 1 is a block diagram of a first embodiment for practicing thepresent invention. NC machining program data for machining a givenworkpiece into a part having a predetermined shape are recorded on an NCtape 101. The NC machining program includes tool selection instructionsat suitable locations, and at the end thereof an instruction M02(program end auxiliary function instruction) or M30 (tape end auxiliaryfunction instruction) indicating the end of the program, or a symbolregistered in advance to indicate the end of the program. A toolselection instruction, it should be noted, is expressed in the formT□□□□, namely by the letter of the alphabet "T" indicating toolselection, and a four-digit numerical value following "T". A toolselection number is specified by the two leftmost digits, and a tooloffset number by the two rightmost digits. A tape reader 102, inresponse to an indication from a control unit (not shown), reads NCmachining data from the NC tape one block at a time and applies the readNC machining data to a decoder 103. The decoder 103 decodes the NCmachining data and delivers a high-level ("1") output on a line L₁ whenM02, M30 or the symbol is discriminated. A counter 104 is incrementedwhenever a "1" appears on line L₁, thereby counting the number W ofmachined workpieces Preset in a preset counter 105 is a number W_(L) ofparts to be machined, the number conforming to the life of theparticular tool. More specifically, when a tool has contributed tomachining a number of parts equivalent to the set number W_(L), this istaken as indicating that the tool nose has sustained wear and is nolonger capable of performing machining correctly in the mannercommanded. A comparator 106 monitors whether the counted value (numberof parts) W in the counter 104 is equivalent to the number W_(L) ofparts to be machined, and produces a signal LRS, which indicates end oftool life when coincidence between W and W_(L) is attained. The countedvalue in counter 104 is cleared by the signal LRS, and the counter 107counts the signal LRS to record the number of times n the signal isgenerated (i.e., the number of times a tool has reached the end of itslife).

Meanwhile, when the letter of the alphabet "T" is discriminated, thedecoder 103 sets the two leftmost digits (tool selection number) in aregister 108 and the two rightmost digits (tool offset number) in aregister 109 When a tool selection instruction is read from the NC tapeand a tool selection number Nt is set in the register 108, an arithmeticcircuit 110 performs the operation given by:

    Nt+Nct·n→Nnt                               (1)

with the result of the operation being delivered as an actual toolselection number Nnt. It should be noted that Nct in the foregoingequation is a tool selection number correction value preset in aregister 111. As a result of the foregoing operations, when the numberof times n a tool has reached the end of its life is zero, the toolselection number Nt of the tool selection instruction is applied to themachine as the actual tool selection number Nnt. If the number of timesa tool has reached the end of its life is one or more, the result ofperforming the operation of Eq. (1) is delivered as the actual toolselection number. Describing a specific case where the tool selectionnumber correction value is 10 and the maximum value of the toolselection number is 30, the actual tool selection numbers will be asshown in FIG. 2, depending upon n, where n=0, 1, 2, . . . and so on. Itis assumed that the tools indicated by the tool selection numbers T0i,T1i, T2i are all of an identical type, so that three identical tools areprepared

It will be apparent from the foregoing that, when n=0 holds, the toolselection number T0i in the NC machining program is delivered intact asthe actual tool selection number. When n=1 holds, T1i is delivered eventhough T0i is the tool selection number in the machining program. Whenn=2 holds, T2i is delivered even though T0i is the tool selection numberin the machining program. From n=3 onward, the tool selection number T0iin the machining program is again produced, after which tool selectionnumbers are delivered in the manner set forth above. Thus, whenever atool reaches the end of its life, the actual tool selection numberchanges in the fashion T0i→T1i→T2i→T0i→T1i→ . . . and so on.Accordingly, if three identical tools are prepared and are assigned toolnumbers T0i, T1i, T2i, then, when tool T0i reaches the end of its life,the succeeding tool T1i is used, and when tool T1i reaches the end ofits life, the succeeding tool T2i is used. Before tool T2i is expended,tool T0i is exchanged for an unworn, new tool, and this new tool T0i isemployed when tool T2i reaches the end of its life. Note that when theresult Nnt of performing the operation of Eq. (1) exceeds the maximumvalue 30, the arithmetic circuit 110 delivers, as the tool selectionnumber, a value obtained by subtracting the maximum value from theresult Nnt. However, it can be so arranged that the the result ofperforming Eq. (1) does not exceed 30. This can be done by providing thecounter 107 with a capacity of three, so that the value counted therebywill undergo a transition given by 0→1→2→0→1→ . . . and so on wheneverthe signal indicating the end of a tool life is generated.

When a tool selection instruction is read from the NC tape and a tooloffset number No is set in the register 109, an arithmetic circuit 112performs the operation given by:

    No+Nco·n→Nno                               (2)

with the result of the operation being delivered as an actual tooloffset number Nno. It should be noted that Nco in the foregoing equationis a tool offset number correction value preset in a register 113. As aresult of the foregoing operations, when the number of times n a toolhas reached the end of its life is zero, the tool offset number No ofthe tool selection instruction is delivered intact to an offsetprocessing unit 114 as the actual tool offset number Nno. If the numberof times a tool has reached the end of its life is one or more, theresult of performing the operation of Eq. (2) is delivered as the actualtool offset number. Describing a specific case where the tool offsetnumber correction value is 10 and the maximum value of the tool offsetnumber is 30, the actual tool offset numbers will be as shown in FIG. 3,depending upon n, where n=0, 1, 2, . . . and so on.

It will be apparent from the foregoing that, when n=0 holds, a tooloffset number "0i" in the NC machining program is delivered intact asthe actual tool offset number. When n=1 holds, "1i" is delivered eventhough "0i" is the tool offset number in the machining program. When n=2holds, "2i" is delivered even though "0i" is the tool offset number inthe machining program. From n=3 onward, the tool offset number "0i" inthe machining program is again produced, after which tool offset numbersare delivered in the manner set forth above. Thus, whenever a toolreaches the end of its life, the actual tool offset number changes inthe fashion "0i"→"li"→"2i"→"0i"→"li"→ . . . and so on.

Accordingly, if three identical tools having different offset values areprepared and are assigned tool numbers T0i, T1i, T2i, and if the offsetvalue of tool number T0i is stored in a dial or offset memory conformingto a tool offset number "03", the offset value of tool number T1i isstored in a dial or offset memory conforming to a tool offset number"13", and the offset value of tool number T2i is stored in a dial oroffset memory conforming to a tool offset number "23", then, whenevertools reach the end of their respective lives, new tools are selectedone after another and offset correction processing in accordance withthe offset value of the new tool is executed.

FIG. 4 is a block diagram of an embodiment in which the presentinvention is applied to a computerized NC apparatus. Tool lifesupervision will be described hereafter with reference to FIGS. 4 and 5.

(a) When a power button on an operator's panel 201 is pressed tointroduce power, a processor 202, under the control of a control programstored in a ROM 203, transfers to a RAM 205: the number W (initiallyzero) of parts machined; the number of times n (initially zero) a toolhas come to the end of its life; the number W_(L) of parts to bemachined, which conforms to tool life; the tool selection numbercorrection value Nct; and the offset number correction value Nco, thesehaving been stored beforehand in a non-volatile parameter memory 204.

(b) Next, pressing a cycle start button (not shown) on the operator'spanel 201 causes the processor 202 to drive a tape reader 206 and readone block of NC data from an NC tape 207.

(c) Thereafter, the processor 202 determines whether the NC data readunder the control of the control program stored in the ROM 203 is M02,which indicates program end.

(d) If the NC data is not M02, then the processor 202 determines whetherthe NC data is a tool exchange instruction T□□□□.

(e) If the NC data is not a tool exchange command, the processor 202executes ordinary NC processing. When such processing ends, theprocessor 202 reads the next block of NC data from the NC tape 207 andrepeats the process steps from step (c) onward.

(f) If the NC data read in the decision step (d) is the tool exchangeinstruction, the processor executes the operations of Eqs. (1), (2) toderive the actual tool selection number Nnt and actual tool offsetnumber Nno, respectively. Let the tool selection number correction valueNct and offset number correction value Nco each be 10, and let themaximum value of the tool selection number and of the offset number be30. Then, if the result of performing the operation of Eq. (1) and ofEq. (2) is 30 or more, values obtained by subtracting 30 from theseresults serve as the tool selection number and tool offset number,respectively.

(g) When the calculations in accordance with Eqs. (1) and (2) end, theprocessor 202 delivers both the tool exchange instruction and thecalculated tool selection number Nnt to a machine tool 301 through adata input/output unit 208.

(h) Upon receiving the tool exchange instruction and tool selectionnumber, the machine tool 301 effects a tool change by means of anautomatic tool change mechanism, not shown.

(i) When the tool change ends, the maching tool 301 delivers a toolchange completion signal to the data input/output unit 208.

(j) The processor 202 constantly monitors whether the tool changecompletion signal has been generated. If generation of the tool changecompletion signal is recogized, the processor 202 drives the tape reader206 and reads the next NC data from the NC tape 207.

(k) The processor determines whether the NC data read is path data andexecutes ordinary NC processing if it is not. If the data is path data,then the processor goes to an offset memory 209 and reads an offsetvalue indicated by the offset number Nno, which is the result ofperforming the operation of Eq. (2). The processor then executeswell-known offset processing.

(1) Next, the processor 202 calculates incremental quantities .sub.Δ X,.sub.Δ Y along the respective axes based on the results of the offsetprocessing, and delivers the incremental values to a pulse distributor210. On the basis of the incremental quantities input thereto, the pulsedistributor 210 performs a pulse distribution operation to generatedistributed pulses XP, YP applied to servo circuits 211X, 211Y. Thelatter drive servomotors 212X, 212Y in response to the distributedpulses XP, YP, thereby to transport a tool or table.

(m) When the tool or table reaches a target position, the processor 202reads the next NC data from the NC tape 207 and repeats the processsteps from step (c) onward.

(n) If the NC data read is found, indecision step (c), to be the programend instruction M02, then the processor 202 performs the operation givenby:

    W+1→W                                               (3)

to update the number W of parts machined.

(o) Next, the processor determines whether the number W of partsmachined has become equal to the number W_(L) of parts to be machined,which number is set in accordance with tool life.

(p) If the number W of parts machined is equal to the number W_(L) ofparts to be machined, then the following operations are performed:

    n+1→n                                               (4)

    0→W                                                 (5)

thereby incrementing the number of times n a tool has come to the end ofits life, and clearing the number W to zero.

(q) After performing the operations of Eqs. (4) and (5), or if W<W_(L)is found to hold in the decision step (o), n and W are stored in theparameter memory 204, thereby ending a series of tool life supervisionprocess steps. In FIG. 4, note that numerals 213, 214 denote address anddata buses, respectively.

According to the present invention, a number of machined parts, whichcorresponds to tool life, is preset, instructions or symbols indicatingprogram end are counted to record the number of parts machined, and alltools used in machining the part are changed when the actual number ofparts machined coincides with the number to be machined, the latternumber corresponding to tool life. Thus, tool life supervision issimplified as there is no need to exercise tool life supervision tool bytool.

In addition, different tool numbers can be assigned to a plurality ofidentical tools, and when a tool comes to the end of its life, the toolnumber of a new tool to be used thereafter can be obtained automaticallymerely by executing the operation indicated by Eq. (1). This greatlysimplifies tool utilization sequence supervision.

Further, the offset number of a new tool put into use when a toolreaches the end of its life can be obtained merely by executing theoperation indicated by Eq. (2), thereby making it possible to simplifyoffset processing as well. Still further, the maximum values of the toolselection number and tool offset number are decided. The arrangement issuch that when the results of performing Eqs. (1), (2) exceed thesemaximum values, values obtained by, for examples the subtraction ofthese maximum values serve as the tool selection number and tool offsetnumber, and such that the tool offset number and tool offset value arechanged in cyclic fashion. Accordingly, tool life supervision issimplified.

It goes without saying that the contents of counters 104, 107 and ofpreset counter 105 and registers 111, 113 in FIG. 1 are saved in anon-volatile memory before electric power is cut off, and that thesecontents are restored after power is introduced. Also, in the foregoing,it was assumed that the tool selection number correction value Nct andtool offset number correction value Nco were both ten. However, if thenumber of tools used in a single machining program is five, then Nct,Nco can be arranged to each have a value of five. That is, if it isassumed that the number of tools used in a single machining programgenerally is m, then it will suffice to set Nct, Nco to m.

Thus, according to the present invention, it is so arranged that toollife supervision for all tools commanded by a single NC machiningprogram can be performed en bloc, and it is unnecessary to perform toollife supervision tool by tool. Therefore, the invention is well-suitedfor application to numerically controlled machine tools.

I claim:
 1. A tool life supervision method in which the life of a toolis monitored and machining is performed by automatically using anothertool when a former tool has reached the end of its life, the methodcomprising the steps of:(a) setting in memory means a number W_(L) ofparts to be machined, which number conforms to tool life, and setting inthe memory means a tool selection number correction value Nct; (b)inserting at an end of an NC machining program at least an instructionor symbol which indicates the end of the program; (c) detecting andcounting the number of times W the instruction or symbol indicating theend of a program is detected; (d) monitoring whether the counted value Wcoincides with a preset number W_(L) of parts to be machined and; (e)counting the number of times n coincidence is achieved and performingthe following operation to determine a tool selection number:

    Nt+Nct·n

wherein NT represents a tool selection number indicated by a toolselection instruction in the NC machining program; and (f) selecting atool by employing the result of the aforesaid operation as an actualtool selection number.
 2. A tool life supervision method according toclaim 1, wherein the counted value W and the numbef n are storedcommonly for all tools commanded by the NC machining program.
 3. A toollife supervision method according to claim 1, wherein tools designatedby the tool selection numbers Nt+Nct·n (n=0, 1, 2, . . . ) identifyidentical type tools.
 4. A tool life supervision method according toclaim 1, wherein the tool selection number correction value Nct isselected to be m when a number of tools used by a single NC machiningprogram is m.
 5. A tool life supervision method according to claim 1,further comprising the steps of:presetting a maximum value of the actualtool selection number; and limiting the result of said operation whenthe result of said operation exceeds the maximum value by subtractingsaid maximum value from the tool selection number determined in step(e).
 6. A tool life supervision method in which the life of a tool ismonitored and machining is performed by automatically using another toolwhen a former tool has reached the end of its life, the methodcomprising the steps of:(a) setting in memory means (i) a number W_(L)of parts to be machined, which number conforms to tool life, (ii) a toolselection number correction value Nct, and (iii) a tool offset numbercorrection value Nco; (b) inserting at an end of an NC machining programat least an instruction or symbol which indicates the end of theprogram; (c) detecting and counting the number of times W theinstruction or symbol indicating the end of a program is detected; (d)monitoring whether the counted value W coincides with the preset numberW_(L) of parts to be machined; (e) counting the number of times ncoincidence is achieved and performing the following operations torespectively determine a tool selection number and an actual tool offsetnumber:

    Nt+Nct·n→Nnt

    No+Nco·n→Nno

wherein Nt represents a tool selection number indicated by a toolselection instruction in the NC machining program and No represents atool offset number; (f) selecting a tool by employing Nnt as an actualtool selection number; and (g) executing tool offset processing byemploying Nno as an actual tool offset number.
 7. A tool lifesupervision method according to claim 6, wherein the counted value W andthe number n are stored commonly for all tools commanded by the NCmachining program.
 8. A tool life supervision method according to claim6, wherein the tool selection number correction value Nct and the tooloffset number correction value Nco are both selected to be m when anumber of tools used by the NC machining program is m.
 9. A tool lifesupervision method according to claim 6, further comprising the stepsof:presetting a first maximum value of the actual tool selection numberand a second maximum value of the actual tool offset number; limitingthe value of Nnt when Nnt exceeds the first maximum value by subtractingthe first maximum value from Nnt to produce an actual tool selectionnumber; and limiting the value of Nno when Nno exceeds the secondmaximum value by subtracting the second maximum value from Nno toproduce an actual tool offset number.
 10. A tool life supervision methodaccording to claim 6, wherein the tools designated by the tool selectionnumbers Nt+Nct·n (n=0, 1, 2, . . . ) identify identical type tools.